Watches with mechanical movements, called “skeleton-watches”, have been known for a long time. A Swiss Patent No. CH 28539 discloses a watch wherein the dial is made of a transparent material, such as glass, mica, or celluloid and allows the mechanism of the movement, and the plates and metal bridges to be seen. The hour symbols are added by any means to the visible surface of the dial. U.S. Pat. No. 4,534,660 and CH Patent No. 690 518 disclose even more “skeletal” watches. In U.S. Pat. No. 4,534,660, the top plate forming the crystal, the plates and the bridges, and the bottom plate form a pile made of a crystalline material, such as sapphire, said plates being machined with apertures or recesses for housing the parts of the movement, so as to make the entire watch mechanism visible. CH Patent No. 690 518 has the same objective, but with a single-piece transparent assembly cage made by ultrasound machining using a sonotrode. This latter document advises affixing the time symbols to the bezel to increase the aesthetic effect.
Between the oldest prior art where the dial is entirely opaque and the aforecited prior art where it is entirely transparent, with the exception of a few marking zones, there are no intermediate solutions for having quite wide opaque zones and complementary transparent zones or vice versa. The teaching of this prior art does not allow shades of colour to be created at the surface of the dial either.